The meat industry, including the poultry processing industry, faced challenges with cost effective handling of sludge (typically referred to as dissolved air floatation (DAF) skimmings) that results from processing. DAF skimmings originates as the watery waste from meat processing and from cleaning of the process facilities. By volume, DAF skimmings is primarily water, but DAF skimmings also contain waste such as bone chips, skin parts, animal by-products, and scraps, of which some is valuable animal fat, protein and other nutrients. Efforts are made to extract at least some of the water from the DAF skimmings, such as by drainage from holding tanks, for subsequent transfer of the at-least partially dewatered DAF skimmings to rendering plants. Dewatering reduces the volume of DAF skimmings that is to be transported by truck and thus lowers the cost of handling processing plant waste. Further, water supply systems often require processing plants to filter and clean the waste water before return to sanitary sewer systems.
The rendering process further dewaters and dries the DAF skimmings and separates fats from valuable bone, protein and nutrients, which are referred to as Secondary Product Nutrients (SPN) that can be sold to mill manufacturers of livestock and aquiculture feed for further beneficial uses and products. However, free fatty acids develop quickly and build-up in the DAF skimmings. As the DAF skimmings deteriorates, free fatty acids build up, and as the free fatty acids increase, the valuable animal fat and protein nutrients decrease and become rancid. High concentrations of free fatty acids prevent further processing and use of the valuable SPN. The SPN all too often wind up in landfills and essentially a profitable by-product for the meat processing industry is thrown away.
There are difficulties with DAF skimmings processing whether for return of water to sanitary sewer systems or for further use of SPN after rendering of the processing wastes. SPN within DAF skimmings is solid sensitive such that it is difficult to break apart properly and de-water. Belt press devices and gravity dewatering process have been developed but there are drawbacks. Primarily, the end result was typically a product that was a prime target for pathogens and free fatty acid growth. This defective product was waste and lacked value but also resulted in unpleasant plant odor. Often DAF skimmings was transferred to landfill without recovery of the lucrative animal by-products.
When SPN is formed, the bonds between the fat, water and solids are generated by chemical polymers and coagulation agents. This allows the removal of fat and solids from wastewater. While most of these compounds may be mechanically separated, a portion of the SPN however is bound tightly by the chemical compounds that combined with an energy source (such as steam injection) that an emulsion is formed. Heretofore, separation of the emulsions into individual parts is accomplished by heat process and by chemical process, and each has unsatisfactory drawbacks.
The heat process applies high heat (above 265 degrees F.) to the emulsions to evaporate a large portion of the water from the compound. The fat and solids can then be separated mechanically. Remaining water is removed, after the mechanical separation is complete, by applying heat again to the individual components for evaporation of the remaining water.
The chemical process introduces a solvent (for example, hexane) to the emulsion. The solvent removes the electrical charge of the compound that is binding the fat, solids and water and allows for mechanical separation.
While these processes accomplish the recovery of the valuable fats, and portions of the water evaporate rather than discharge into sanitary and water treatment systems, and the separated solids reduce the volume for landfill or other uses, the processes have high energy and high chemical costs. Absent recoverability equipment for accomplishing reuse, the cost for chemical separation may be prohibitive. Also, most of the chemical solvents are hazardous air pollutants and require close monitoring and control to prevent improper release.
My earlier U.S. Pat. No. 8,163,176 discloses an apparatus and method for cracking the DAF skimmings to break apart the fat, protein and solids from the waste and water. The fat and solids float to the top surface of the water and problematic pathogens and bacteria evaporate. The water drains from the stratified DAF skimmings, and the resulting decanted solids contain the profitable SPN with animal fat, protein and other nutrients and beneficially, with reduced water content, have a significantly reduced volume for transport. The decanted water may be cleaned appropriately for return to sanitary sewer systems. The decanted solids have high quality SPN content, reduced free fatty acid growth, and decreased odor.
The disclosed apparatus for cracking DAF skimmings, while successful in reducing water content, nevertheless does not provide for the optimal separation of water from the SPN within water waste DAF skimmings for large commercially significant meat processing facilities. Accordingly there is a need in the art for an improved apparatus and method for separation of the fats, solids and water while reducing energy and chemical costs. It is to such that the present invention is directed.